The present invention relates to a base station equipped with an interference measuring device, and more particularly, to a method of testing the measuring device to determine if the interference measuring device is working properly.
In cellular communication systems, frequency reuse plans allow the same frequency to be used more than once within the system. Rather than use a single high power transmitter to cover a large geographic area, cellular systems employ a large number of low-power transmitters that broadcast signals in relatively small geographic areas referred to as cells. Each cell may be only a few miles across, and theoretically could be as small as a few city blocks. By reducing the coverage area of the transmitter and creating a large number of cells, it is possible to reuse the same frequency in different cells. Thus, a single frequency may be used multiple times throughout the entire cellular system to increase system capacity.
To avoid co-channel interference, cells operating on the same frequency are spatially separated so that a mobile terminal operating within a cell receives desired signals at a higher level than any potential interfering signals from co-channel cells. Cells operating at different frequencies are placed between any two co-channel cells. In general, the power of any interfering signal diminishes with increasing distance between interfering users. A carrier frequency can be reused if the interference level is reduced sufficiently by separation between the co-channel cells. The interference level is measured by the carrier power to interference power ratio, C/I.
Interference is one of the major limiting factors in the performance of a mobile communication network. Ideally, interference between cells should be minimized. However, there are presently few techniques by which interference between cells can be measured. One technique currently being used involves sending a technician to the field to make phone calls and evaluate signal quality. Another technique, proposed by the assignee of the present invention, involves the base stations listening to access requests made by mobile terminals on an access channel in neighboring cells. A base station using this method tunes one of its receivers to an access channel of a neighboring cell and performs measurements on the access requests made by mobile terminals in the neighboring cell. This functionality is sometimes referred to as a Listening Control Channel (LICC). With enough measurements from various base stations within a measurement area, a mobile switching center can estimate a carrier-to-interference ratio.